It is well known to use coalescing media, such as knitted wire mesh pads and the like, for mist elimination to coalesce small droplets of fluid which are entrained in a vapor flow. The coalescing media acts to collect liquid particles on the fibers and to coalesce the droplets into liquid films and large droplets which can then move through the coalescing media under the drag force of the gas and downward by capillary action and gravity through the coalescing media. Typically, the coalesced collected liquid drains off the downstream face of the coalescing media to a collection zone.
It is known to position a separation vessel downstream of a gas compressor to remove lubricating oil mists and droplets which have become entrained in the high pressure flow of gas leaving the compressor.
Separation vessels are typically either vertical or horizontal in orientation. In the case of vertical separation vessels, a gas flow velocity as calculated by the Souders-Brown equation [Vallowable ft/sec=K(PL−Pg)/Pg)1/2] with a K of about 0.30 to about 0.35 feet/second is typically a maximum velocity to avoid flooding of mesh pad type coalescing media commonly used. As described in AMISTCO Technical Bulletin 105, www.amistco.com/spanish/tech105.htm, a calculated vapor load factor or “K” factor as defined by the Souders-Brown equation utilizes the K factor for determining the flux cross section area of a mist eliminator or knockout drum. In the case of horizontal gas flows, the K value may be increased to about 0.5 using conventional mesh pads before flooding occurs.
If, in the case of a horizontal gas flow, the gas flow velocity is increased beyond the typically accepted value of K=0.5, the droplets which collect on the downstream face of the coalescing media often become re-entrained in the gas flow negating the separation performed by the coalescing media. Thus, conventionally large horizontal vessels have been required to keep the flow velocity below that at which the droplets will not re-entrain in the gas flow.
Thus, there is a need for apparatus and systems for mist elimination that minimize the size of the vessel required so as to reduce costs and environmental impact and increase the efficiency of mist elimination in gas flows.